<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <meta http-equiv="X-UA-Compatible" content="ie=edge" />
    <title>Document</title>
  </head>
  <!-- link会阻塞dom的渲染 不会阻塞他的解析 link之前浏览器能把dom解析完成并且渲染 渲染到一半时候遇到link阻碍渲染就会停止，继续解析link的css解析完后再继续渲染后面的h1 -->
  <style>
    h1 {
      color: red;
    }
  </style>
  <body>
    <h1>hello World</h1>
    <link
      href="https://cdn.bootcss.com/bootstrap/4.0.0-alpha.6/css/bootstrap.css"
      rel="stylesheet"
    />
    <h1>hello World</h1>
  </body>
</html>
